1. Field of the Invention
The present invention relates to a paper conveying mechanism for a printing apparatus and is particularly suitable for a clamshell printer in which a paper conveying path is formed by a combination of paper-thickness-direction regulating guides and paper-width-direction regulating guides.
2. Description of the Related Art
Hitherto, there have been proposed printers in each of which continuous-form paper that is in a roll is conveyed along a paper conveying path. In such a printer, printing is performed on the continuous-form paper with a print head mounted above the paper conveying path, and the paper is then cut into a piece having a predetermined length by an automatic cutter. In general, such a printer includes a guide mechanism provided around the paper conveying path so that the continuous-form paper is properly conveyed (see Japanese Unexamined Patent Application Publication No. 2011-136472, Japanese Patent No. 2706193, Japanese Unexamined Patent Application Publication No. 2007-99458, and Japanese Patent No. 4183309, for example).
Japanese Unexamined Patent Application Publication No. 2011-136472 and Japanese Patent No. 2706193 each disclose a configuration in which paper is guided by an upper guide and a lower guide that are arranged in a paper thickness direction. Japanese Unexamined Patent Application Publication No. 2007-99458 and Japanese Patent No. 4183309 each disclose a configuration in which paper is guided by side guides that are arranged in a paper width direction so that the skewing of the paper is prevented. Examples of the printer having a paper conveying path formed by paper-thickness-direction regulating guides and paper-width-direction regulating guides include a so-called clamshell printer.
In a general clamshell printer, an upper guide corresponding to a paper-thickness-direction regulating guide is mounted on a printer cover that is openable and closable while a lower guide corresponding to another paper-thickness-direction regulating guide and paper-width-direction regulating guides are mounted on a printer body. When paper is set in a paper holder mounted on the printer body and the printer cover is then closed, a paper conveying path is formed by a combination of the paper-thickness-direction regulating guides and the paper-width-direction regulating guides.
FIG. 6 is a front view of a known printer and illustrates the positional relationship between an upper guide 101 and side guides 102. In FIG. 6, the lower side of the page is defined as the printer bottom side, and the upper side of the page is defined as the printer top side. In the printer illustrated in FIG. 6, paper that is in a roll is set in a paper holder 103 and is conveyed toward the printer top side. The paper is conveyed along the conveying path and discharged from a discharge port (not illustrated) on the front side of the printer. During the conveyance, the paper is guided by the upper guide 101, a lower guide (not illustrated), and the side guides 102 forming paper-width-direction ends of the paper conveying path.
As described above, in the clamshell printer, the upper guide 101 is accommodated between the side guides 102 forming the paper-width-direction ends of the paper conveying path as illustrated in FIG. 6. In such a configuration, if a gap between the upper guide 101 and each of the side guides 102 is completely eliminated, the upper guide 101 and the side guides 102 interfere with each other, causing a possible problem with the opening or closing of the printer cover. To prevent such a problem, a gap needs to be provided between the upper guide 101 and each of the side guides 102 forming the paper-width-direction ends of the paper conveying path.
If a large gap is provided, however, the paper may be taken into the gap and thus be folded. Particularly, a flexible thin paper tends to be folded more frequently. To prevent the paper from being taken into the gap, the gap provided between the upper guide 101 and each of side guides 102 forming the paper-width-direction ends of the paper conveying path needs to be reduced.
The size of the gap can be reduced by improving dimensional accuracy of each of the components of the printer. Even if the dimensional accuracy of the components is improved, however, a large gap is possibly produced when the printer cover is closed. FIG. 7 is a schematic sectional view of the printer illustrated in FIG. 6, seen from the printer bottom side. The upper guide 101 leans toward one side in the paper width direction in a space between the side guides 102 forming the paper-width-direction ends of the paper conveying path, thus producing a larger gap on one side. Most printer covers are designed with some play so as to be openable and closable smoothly. Such play causes deflection of the upper guide 101 toward one side in the paper width direction. There has been a problem of the paper being taken into the gap and folded.